It is desirable to scan the contents of objects such as, for example bottles, at security and customs checkpoints to gain information about content based on radiation received at a detector after interaction with the object and obtain an indication that the contents of the object do not constitute a threat to security or a breach of customs regulations. It is also desirable to scan the contents of objects for other purposes such as quality control, content verification, degradation monitoring etc.
To ensure that the contents of an object are what they are claimed to be, it may be useful to scan the object and contents so that a high energy ionising radiation beam traverses a cross section of the object. It can be possible to obtain an indication of the materials composition from a numerical analysis of the resultant transmitted radiation beam intensity data and to compare the results of that analysis with a reference data set relating to materials of known composition.
The transmission of x-rays through a material can be given by the exponential attenuation law, as follows:I/Io=exp[−(μ/ρ)ρt]  (1)where                μ/ρ=Mass attenuation coefficient. A material constant which is characteristic of the weighted elemental composition of a material;        I=final intensity;        Io=Initial intensity;        ρ=density of the material; and        t=thickness of the material.        
Thus by looking at the variation in the x-ray transmission as a function of changes in the thickness “t” of a material, for example, deductions can be made about the mass attenuation coefficient and the density of the material. These two parameters are characteristic of different materials and so materials identification becomes possible.
Instrumentation has been developed which is intended to non-invasively identify target liquids and like materials (that is, materials having similarly generally homogenous composition throughout) held within sealed containers. The target liquids or like materials may be liquids or like materials which pose a security threat if carried on-board an aircraft, liquids containing dissolved narcotics, or liquids requiring quality control, for example. According to techniques disclosed in our co-pending International Patent Application No. PCT/GB2008/050711 (Publication No. WO2009/024818), a container may be irradiated with a beam of x-rays and the transmission characteristics of the container and its liquid contents measured using an energy selective detector such as cadmium telluride or germanium.
The transmission characteristics of various contained materials held in a variety of containers could be recorded and held in a database. The database could then be used for comparison with in situ scanning of containers and contents to look for matched transmission characteristics and, therefore, target materials could be identified. One drawback of such a system would be that the database, to be effective, would be required to hold a very large amount of data relating to the transmission characteristics of a variety of liquids or like contents and a variety of containers. Interrogation of the database would be time consuming and, therefore, unsuitable for many intended uses, such as in airport security where time is often of the essence.
When the object being scanned is a contained material which by its nature will be expected to have a single generally homogeneous composition, for example being a fluid composition such as a liquid as above described in a container, both the contained material and the container itself are subject to individual component variables, such as: the type of contained material, the composition or concentration of a contained material, the path length of high energy ionising radiation in the contained material, the material from which the container is made, and the thickness of the wall of the container, for example.
In order to provide a faster and accurate matching of data from a numerical analysis of resultant transmitted radiation beam intensity data from a scan of a container and its contents, it would be desirable to remove the component of the data relating to the container itself, thereby resulting in data relating to the contents only which may then be compared with a reference data set relating to content materials of known composition.
There is a need for an improved analytical tool for non-invasively identifying a contained material such as a liquid within a container.
Furthermore, there is a need for an improved method, system and apparatus for undertaking scanning of objects and their contents using high energy ionising radiation, where the identification and analysis of the contents is made without interference from the object itself.